Moved Transparent Color button to ContextBar

Implemented SelectionSettings class

Transparent Color button for moving pixels moved from status bar to
context bar.  Current Transparent Color stored by new SelectionSettings
class, retrievable from ISettings.

Also implemented Observer classes for existing Settings interfaces for
future use.

StatusBarObserver interface and supporting code removed from StatusBar.
Merge pull request #9 from DocHoncho/ui-dev-squashed

Moved Transparent Color button to ContextBar, implemented SelectionSettings class